1. Field of the Invention
The present invention relates to electronic components and a method for producing the electronic components, and more particularly to an electronic component such as a surface acoustic wave device (SAW device), a high frequency device, and a module or sub-module including an SAW device and a method for producing these devices.
2. Description of the Related Art
(First Conventional Example)
The structure of a conventional surface acoustic wave device 1 is shown in FIG. 1. In the surface acoustic wave device 1, a surface acoustic wave element (chip) 3 is disposed and die bonded within a ceramic package 2 of a cavity structure with a recess formed therein. The surface acoustic wave element 3 is electrically connected to electrodes 5 disposed on the ceramic package 2 through wires 4. The top surface of the ceramic package 2 is covered by a plate-shaped cap 6, and the surface acoustic wave element 3 is hermetically sealed by welding the external peripheral portion of the cap 6 on the top surface of the ceramic package 2 via a KOVAR ring 7.
In such a surface acoustic wave device 1, since a material such as Al, which has a low degree of moisture tolerance, is used as the electrode material of the surface acoustic wave element 3, corrosion of the electrodes is retarded by hermetic sealing of the surface acoustic wave element 3. A space is formed between the surface acoustic wave element 3 and the cap 6 so that elastic oscillation of the surface acoustic wave element 3 is not prevented.
However, in such a surface acoustic wave device 1, because the ceramic package 2 of a cavity structure with a recess formed thereon is required, the cost thereof is expensive. The mounting area and height (thickness) thereof are increased by the volume of the ceramic package 2 relative to the size of the surface acoustic wave element 3, so that dense mounting of the surface acoustic wave devices 1 and so forth and miniaturizing of an apparatus in which the surface acoustic wave device 1 is assembled are prevented. Furthermore, since the ceramic package 2 is used, in addition to the manufacturing processes of the ceramic package 2 itself and the KOVAR ring 7, the connecting process between the ceramic package 2 and the KOVAR ring 7, die bonding of the surface acoustic wave element 3, welding between the KOVAR ring 7 and the cap 6, etc., are required, such that the manufacturing processes are complicated and expensive.
(Second Conventional Example)
The structure of another conventional surface acoustic wave device 11 is shown in FIG. 2. In the surface acoustic wave device 11, a surface acoustic wave element (bare chip) 13 is flip-chip mounted face down on a wiring substrate 12; and a bump 14 disposed on the top surface of the surface acoustic wave element 13 is connected to a substrate electrode 15 disposed on the wiring substrate 12. A space between the surface acoustic wave element 13 and the wiring substrate 12 is hermetically sealed by a sealing resin 18 so as to prevent corrosion of the bump 14 and the substrate electrode 15 and damage to the connecting portions due to thermal stress differences. Flowing of the sealing resin 18 before curing is also prevented by a resin-flow-preventing membrane 19 formed on the top surface of the wiring substrate 12.
However, in the surface acoustic wave device 11, the sealing resin 18 charged between the wiring substrate 12 and the surface acoustic wave element 13 has a specific dielectric constant of 3 to 4, so that the dielectric characteristic thereof considerably affects the transmission loss and reflecting characteristics of the surface acoustic wave device 11. Also, the long time required for charging the sealing resin 18 between the wiring substrate 12 and the surface acoustic wave element 13 prevents the manufacturing process from being streamlined. Further, since the surface of the surface acoustic wave element 13 is sealed by the resin, the resulting restraint of the Mechanical Elastic Oscillation thereof may cause deterioration of the characteristics of the surface acoustic wave device 11.
(Third Conventional Example)
In order to address the foregoing problems, a surface acoustic wave device 21 using both a ceramic package with a cavity structure, and a bump connection, is used without a sealing resin which would prevent elastic oscillation of a surface acoustic wave element and increase its transmission loss. Moreover, such a structure is capable of being miniaturized. Such a surface acoustic wave device 21 is shown in FIG. 3. In the surface acoustic wave device 21, a surface acoustic wave element 23 is disposed face down within the ceramic package 22 similar to the described one in FIG. 1; a bump 27 disposed on the top surface of the surface acoustic wave element 23 is connected to an electrode portion 24; and the outer peripheral bottom surface of a cap 26 is connected on the ceramic package 22 via a KOVAR ring 25.
In the surface acoustic wave device 21 of such structure, since the surface of the surface acoustic wave element 23 is not sealed by a resin, the surface oscillation of the surface acoustic wave element 23 is uninhibited and the characteristics of transmission, reflection, etc., in the surface acoustic wave device 21 are not deteriorated by a sealing resin. Although the ceramic package 22 is used, the need for a space for bonding the wire is eliminated by the bump connection so that the ceramic package 22 can be miniaturized.
However, in such a surface acoustic wave device 21, although the ceramic package 22 is unitized with the surface acoustic wave element 23 by the bump connection, it is not different from the first conventional example in the respect that it also uses the ceramic package 22, so that the surface acoustic wave device 21 cannot be miniaturized substantially more than the first conventional example.
(Fourth Conventional Example)
Accordingly, a structure shown in FIG. 4 has been disclosed (Japanese Unexamined Patent Publication No. 9-162690) as a surface acoustic wave device 31 which neither uses the ceramic package nor has a sealing resin which restrains elastic oscillation of a SAW element""s surface, thereby providing a highly reliable SAW device which can be miniaturized.
In the surface acoustic wave device 31, interdigital electrodes (not shown) and an input-output electrode 33 are disposed on the surface of the surface acoustic wave element 32 and a bump 34 in turn is formed on the input-output electrode 33. An element-side seal ring 35 is disposed on the periphery of the surface acoustic wave element 32. This surface acoustic wave element 32 is laid face down on a mounting substrate 36 so that the bump 34 is connected to a pick-out electrode 37 disposed in the mounting substrate 36 and the element-side seal ring 35 is connected to a substrate-side seal ring 38 on the mounting substrate 36 as well. A space 39 between the surface acoustic wave element 32 and the mounting substrate 36 is sealed by the connection between the element-side seal ring 35 and the substrate-side seal ring 38. The space 39 is sealed in addition by a sealing resin 40 which is coated from the back side of the surface acoustic wave element 32 so as to encapsulate the surface acoustic wave element 32, and which further provides shock protection as well.
In the surface acoustic wave device 31, the surface acoustic wave element 32 is sealed by coating the liquid sealing resin 40 on the entire surface acoustic wave element 32 and then curing the sealing resin 40. As the sealing resin 40, a conventional molding resin including a volatile solvent is used. (In the embodiment of the above-mentioned unexamined patent publication, a CRP series resin from Sumitomo Bakelite is used.) Such a sealing resin 40 is an insulator. However, in a surface acoustic wave device, a countermeasure against electromagnetic radiation is generally required, especially at higher frequencies. When it is sealed by an insulated sealing resin like that used in the surface acoustic wave device 31, it is likely to be affected by electromagnetic radiation and fail to function normally when being used at a high frequency of over 100 MHz.
In the surface acoustic wave device 31, since the surface covered by the sealing resin is curved, when the surface acoustic wave device 31 is automatically mounted by a vacuum-type chip mounter, the vacuum attraction by the chip mounter is not stable so that frequent mis-mounting may occur.
In such a surface acoustic wave device 31, the element-side and substrate-side seal rings 35 and 38, made of Au for example, are joined and unitized together by reflow-soldering both of them after they are tentatively crimped together.
However, to tentatively crimp them together, the element-side and substrate-side seal rings 35 and 38, made of Au, must be heated to approximately 250 to 400xc2x0 C. When the surface acoustic wave element 32 is made of highly pyroelectric material (LiTaO3 or LiNbO3), the surface acoustic wave element 32 is likely to be damaged by pyroelectricity due to the heating. The pyroelectric damage causes a problem in that characteristics of the surface acoustic wave element 32 are adversely affected.
Furthermore, the substrate-side seal ring 38 and the element-side seal ring 35 are then reflow-soldered, after the tentative crimping mentioned above, in order to secure the hermeticity between the surface acoustic wave element 32 and the mounting substrate 36. However, since the melting point of Au is approximately 1000xc2x0 C., when heating for reflow soldering, the element-side seal ring 35 and the substrate-side seal ring 38 are required to be heated to approximately 1000xc2x0 C. or higher. In the surface acoustic wave device 31, Al is generally used as wiring material, having an approximate melting point of 660xc2x0 C., which means that the Al wiring will be melted by the reflow heating. When the Al wiring is cut off in this manner, the required electric characteristics cannot be obtained, resulting in producing defective surface acoustic wave devices 31.
The present invention can solve the problems associated with the conventional devices and provides a small-sized enclosure-type electronic component of simple structure having excellent electric characteristics, and also provides a method for producing an electronic component in which high yield electronic components can be produced without defective products.
An electronic component comprises a substrate having a surface on which an electrode is formed and a circuit element having a surface on which a circuit is formed. The circuit element is held such that the surface of the circuit element and the surface of the substrate are opposed to each other. A bump electrode joins the circuit on the circuit element and the electrode on the substrate together, and a sealing material joins the circuit element and the substrate together at the periphery of the space between the circuit-forming surface of the circuit element and the substrate. The space between the circuit-forming surface of the circuit element and the substrate is hermetically sealed by the circuit element, the substrate, and the sealing material.
In this electronic component, a circuit element and a substrate form the component package; a space between the circuit element and the substrate is formed by a bump electrode; and the space between the circuit element and the substrate is sealed by the circuit element, the substrate, and a peripheral sealing material. Therefore, a ceramic package is not required, so that the electronic component can be miniaturized and the cost can be reduced. Furthermore, since the top surface of the circuit element is not covered by a sealing material, the surface thereof can be smoothed, resulting in preventing mounting mistakes during mounting electronic components by an automatic mounter such as a vacuum-type chip mounter.
Advantageously, a low-temperature soldering material such as solder, or an adhesive, is used as the sealing material. xe2x80x9cLow-temperaturexe2x80x9d in this context means that the soldering material melts at a temperature below the melting point of Au, and furthermore, at a low enough temperature to avoid the problems described above. Since the circuit element and the substrate can be joined together at a comparatively low temperature, the circuit element will not be damaged by the heat, enabling the incidence of defective products to be reduced. When a soldering material such as solder or an adhesive is used as the sealing material, the space between the circuit element and the substrate can securely and hermetically be sealed even if the top of the circuit element is not covered by a sealing resin.
The size of the circuit element may be approximately the same as the size of the substrate in the electronic component.
In the electronic component of such structure, the electronic component can be miniaturized by minimizing the size of the substrate, so that a miniature electronic component can be formed.
The bump electrode may be formed of Au as a principal ingredient. When the bump electrode formed of Au as a principal ingredient is used, the joining can easily be achieved and resistance across the joined portion can be reduced as well.
A method for producing electronic components according to an embodiment of the present invention, comprises the steps of: disposing a bump electrode on either a circuit formed on a circuit element or an electrode disposed on a substrate; disposing a sealing material having a smaller height than said bump electrode on the periphery of either the surface on which the circuit is formed on the circuit element or the substrate so as to surround the circuit formed on the circuit element; disposing the surface on which the circuit is formed so as to oppose the substrate; grounding the circuit via the electrode on the substrate by placing the circuit in contact with the electrode on the substrate through the bump electrode; connecting the circuit to the electrode on the substrate through the bump electrode by applying pressure to the bump electrode; and hermetically sealing the periphery of the space between the circuit element and the substrate with the sealing material.
When an electronic component is produced in this manner, since the circuit is grounded by making contact with the circuit on the substrate via the bump electrode, pyroelectric charge produced in the circuit element when joining the circuit element to the substrate can be dissipated via the bump electrode from the substrate side to ground, so that pyroelectric damage of the circuit element can be prevented.
The circuit element and the substrate are joined together by simultaneously depositing the bump electrode and the sealing material, so that the manufacturing process of the electronic component can be simplified to increase the manufacturing efficiency.
The method may further comprise the steps of joining and unitizing a plurality of circuit elements together on the substrate, the substrate having a size corresponding to a plurality of circuit elements; and then separating the substrate on which the plurality of circuit elements are mounted, to form a plurality of individual electronic components.
In this embodiment, plural electronic components can be produced all at once, so that the efficiency of production of the electronic components can be increased.
For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.